During drilling operations, drilling mud may be pumped into the wellbore. The drilling mud may serve several purposes, including applying a pressure on the formation, which may reduce or prevent formation fluids from entering the wellbore during drilling. For various reasons, sufficient the pressure in wellbore may not be maintained or achieved. When this happens, the formation fluid may enter in the wellbore and mix with drilling fluid. The formation influx fluid commonly has a lower density than the drilling fluid; thus, the hydrostatic pressure in the well is further reduced by the influx of the formation fluid, resulting in an increase in the rate at which the formation fluid flows into the wellbore.
Eventually, the formation fluids mixed with the drilling fluid may reach the surface, resulting in a risk of fire or explosion if hydrocarbon (liquid or gas) is contained in the formation fluid. To control this risk, pressure control devices are installed at surface. For example, the blowout preventer (BOP) may be attached onto the wellhead and a rotary control device (RCD) may be attached on the top of the BOP to avoid the influx fluid reaching the rig floor, as well as allowing pressure management inside the wellbore.
The BOP and/or RCD may include seals to control fluid flow from the wellbore. The seals may include elastomeric elements, which are typically pressed between two rigid (metal) surfaces, e.g., between a pipe ram and a pipe, to form a seal. The wear rate of the elastomeric elements, and/or of the metallic surfaces, may increase during use, based on a variety of factors such as particulates in the environment, the roughness of the metal surface, pressure differential across the seal, etc. Accordingly, the pipe ram seals are often considered a safety mechanism, useful for at most a few actuations, after which the pipe ram seals are typically replaced.
Furthermore, during drilling process, some drill pipe connections at the top of the drill string may be broken, to add or remove drill pipe in the drill string. When the connection between two pipes, or between the top drive and a pipe, is broken during trip-in or trip-out, the pumping of mud generally ceases while a new connection is made. Stopping the mud flow may risk the aforementioned loss of over-pressure and the risks of hazardous conditions that come with it. Further, cuttings may settle in the annulus between the drill string and the wellbore, which may increase the risk of stuck-pipe. Additionally, the filter cake at the bore wall may be affected with risk of additional invasion in some formations, which may reduce productivity along the reservoir, as well as creating a risk for wellbore instability. In addition, gas pressure may rise when the mud no longer circulates through the drill string. Thus, it may be desirable to maintain continuous circulation in the wellbore during the trip-in and trip-out processes.